For people traveling to more than one country in Europe the freedom to move without restriction from one nation to another is an improvement over the past when there were customs controls at every border and each country issued its own visa. Easy movement between countries for citizens of Europe as well as those of the United States, Canada and a number of other countries is enabled by the Schengen Treaty.

Since 1995 visitors from those countries can travel freely inside the Schengen Zone without applying for a visa for up to 90 days within a 180 day period. That freedom is also a limitation: staying longer than 90 days is illegal and can result in severe penalties. As I planned the journey I’m taking now I spent many hours working out plans that would allow me to stay for more than six months without being inside the zone for more than 90 days.

At present 26 countries are in the Schengen Zone. Most but not all of them are member states of the European Union. Seven EU countries are not in the Zone: United Kingdom, Ireland, Croatia, Montenegro, Cyprus, Romania and Bulgaria. At this time Croatia and Montenegro are working toward becoming member states next year; Bulgaria and Romania are also working to become Schengen Zone countries. Switzerland, Norway, and some smaller countries are not in the E.U. but are member states of the Schengen Zone.

I’ve been moving in and out of the Zone since January. Today I’m heading to Estonia and Latvia for a few days. If it weren’t for the 90 day limit I’d be staying there much longer and traveling in Scandinavia as well. When I leave Latvia I’m going to Ukraine for a couple of weeks, in part because its outside the Zone. After that I plan to spend two months in Ireland before returning home. I have used a spreadsheet to count my days in the Zone when planning my journey.

Here’s much more information about the Schengen Treaty and the Zone:
This site has detailed information: https://www.schengenvisainfo.com/schengen-visa-countries-list/
There are several “Schengen Zone calulators” on the web; I like this one best: http://adambard.github.io/schengencalc/
This one is also good: https://www.everyoneinbetween.com/schengen-visa-calculator/
Google “Schengen Zone” to find many references, calculators and explanations on the web.